JP2007292013A - Particulate filter state detection device - Google Patents

Abstract

An apparatus for accurately determining the state of a particulate filter during a transition of an internal combustion engine is provided.
An apparatus for detecting a state of a particulate filter for an internal combustion engine provided by the present invention provides a particulate filter provided in an exhaust system of the internal combustion engine and an exhaust flow rate for detecting a signal correlated with the exhaust flow rate of the internal combustion engine. Detecting means, differential pressure detecting means for detecting the differential pressure across the particulate filter, and a ratio of the change amount of the signal correlated with the exhaust flow rate and the change amount of the differential pressure in a transient state of the internal combustion engine; And a state determining means for determining the state of the particulate filter in comparison with the threshold value.
[Selection] Figure 5

Description

  The present invention relates to an apparatus for detecting the state of a particulate filter that collects particulate matter (particulates) in exhaust gas in an internal combustion engine.

  In general, an internal combustion engine, particularly a diesel engine, discharges particulate matter (particulates, hereinafter referred to as “PM”) during operation. A particulate filter is attached to the exhaust system of the diesel engine so that the PM is not discharged into the atmosphere. The particulate filter collects PM when the exhaust gas passes through fine holes in the filter wall and escapes to the adjacent passage.

  There may be a case where the particulate filter cannot collect PM due to a loss of the particulate filter. In order to detect such a failure state, it is desirable to estimate the state of the particulate filter from the sensor information.

  Patent Document 1 discloses a method of detecting a signal corresponding to the differential pressure across the particulate filter and the exhaust flow rate, and determining clogging of the particulate filter according to the ratio of these two values.

In Patent Document 2, the PM amount accumulated in the particulate filter is calculated based on the differential pressure across the particulate filter and the volume flow rate of the exhaust gas, and the start determination of the regeneration process is performed based on the PM amount. And a method for determining a failure of the particulate filter based on a temporal change in the PM amount is disclosed.
JP-A-57-159519 JP-A-8-284644

  The characteristic of the state of the particulate filter clearly appears during transient operation such as acceleration or deceleration. An object of the present invention is to provide an apparatus that can accurately determine the state of a particulate filter during a transition of an internal combustion engine.

  An internal combustion engine particulate filter state detection device provided by the present invention includes a particulate filter provided in an exhaust system of an internal combustion engine, an exhaust flow rate detection means for detecting a signal correlated with the exhaust flow rate of the internal combustion engine, A differential pressure detecting means for detecting a differential pressure before and after the particulate filter; and a ratio of a change amount of a signal correlated with an exhaust flow rate and a change amount of the differential pressure in a transient state of the internal combustion engine; And a failure determination means for determining failure of the particulate filter.

  According to the present invention, the state of the particulate filter can be accurately determined at the time of transition of the internal combustion engine in which the characteristics of the state of the particulate filter clearly appear.

  In one embodiment of the present invention, the signal correlated with the exhaust flow rate is the pressure in the intake pipe of the internal combustion engine.

  In one embodiment of the present invention, the state determination means compares the ratio of the change amount of the signal correlated with the exhaust flow rate and the change amount of the differential pressure with a first threshold value, and the failure of the particulate filter And the ratio of the change amount of the signal correlated with the exhaust flow rate and the change amount of the differential pressure is compared with the second threshold value, and it is determined that the particulate matter in the particulate filter is excessively deposited. To do.

  In one embodiment of the present invention, the first threshold value is set according to the amount of particulates accumulated in the particulate filter, and the second threshold value is set to the residual amount of ash in the particulate filter. Set accordingly. Accordingly, the state of the particulate filter can be accurately detected in consideration of the effects of the PM accumulation amount and the ash residual amount.

  In one embodiment of the present invention, the state determination means integrates the deviation between the previous value and the current value of the ratio between the change amount of the signal correlated with the exhaust flow rate and the change amount of the differential pressure, and the integrated deviation is predetermined. When the threshold value is equal to or greater than the threshold value, a failure of the particulate filter is determined. Thereby, the failure of the particulate filter can be accurately detected based on the characteristic of the amount of change in the differential pressure when the particulate filter is lost.

  Next, an embodiment of a particulate filter state detection device according to the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a diesel engine mounted on a vehicle and a control device thereof according to an embodiment of the present invention.

  The diesel engine 11 is a direct injection engine that spontaneously ignites by injecting high-pressure fuel into the combustion chamber of each cylinder. The diesel engine 11 controls the output by adjusting the fuel injection amount and injection timing of an injector (not shown) that is attached to each cylinder and injects fuel. The injector injects fuel at an optimal timing based on a control command from an electronic control unit (hereinafter referred to as “ECU”) corresponding to the operating state.

  The ECU 13 includes an input interface 13a that receives data sent from each part of the vehicle, a CPU 13b that executes calculations for controlling each part of the vehicle, a memory 13c having a read-only memory (ROM) and a random access memory (RAM). And an output interface 13d for sending a control signal to each part of the vehicle. The ROM of the memory 13c stores a program for controlling each part of the vehicle and various data. A program for detecting the state of the particulate filter according to the present invention is stored in this ROM. The ROM may be a rewritable ROM such as an EPROM. The RAM is provided with a work area for calculation by the CPU 13b. Data sent from each part of the vehicle and control signals sent to each part of the vehicle are temporarily stored in the RAM.

  Various signals such as sensor output sent to the ECU 13 are transferred to the input interface 13a and subjected to analog-digital conversion. The CPU 13b processes the converted digital signal in accordance with a program stored in the memory 13c, and generates a control signal for sending to each part of the vehicle. The output interface 13d sends these control signals to each element that controls the operation of the engine.

  A diesel particulate filter (hereinafter referred to as “DPF”) 17 is attached in the exhaust pipe 15 of the diesel engine 11. The DPF 17 is composed of a porous filter wall having heat resistance such as ceramic and metal nonwoven fabric, and has a number of flow paths that form an exhaust flow path in the exhaust flow direction. The porous pore diameter is about 10 microns, and particulate matter (particulates; hereinafter referred to as “PM”) contained in the exhaust gas is collected when the exhaust gas passes through the porous filter wall.

  Each of the exhaust flow paths of the DPF 17 is closed at either the upstream end or the downstream end in the exhaust flow direction. A flow path whose upstream end is closed and a flow path whose downstream end is closed are alternately arranged adjacent to each other. For this reason, the exhaust discharged from the exhaust port of each cylinder flows into the flow path in which the upstream end of each DPF is released (the downstream end is closed), and the porous filter wall separating the flow paths is used. It passes through the flow path that has passed through the downstream end and flows out of the DPF from the downstream end.

  Since the PM collected in the DPF 17 deteriorates the filter performance as the amount of accumulation in the filter increases, it is necessary to periodically regenerate the DPF 17. The PM deposited in the DPF 17 is burned by controlling the temperature in the filter to a high temperature and removed from the DPF 17. In order to increase the temperature in the filter, a known method for increasing the exhaust temperature such as post injection, intake shutter valve closing, or EGR introduction is performed.

  A differential pressure sensor 19 is connected to the upstream side and the downstream side of the DPF 17 via a pressure introduction pipe. The differential pressure sensor 19 outputs a signal corresponding to the differential pressure across the DPF 17 to the ECU 13. The differential pressure upstream and downstream of the DPF 17 is characterized by increasing with the accumulation of PM in the filter. The ECU 13 can estimate the PM accumulation amount in the DPF 17 using the output of the differential pressure sensor 19. Further, the ECU 13 can estimate the residual amount of ash remaining in the DPF 17 based on the output of the differential pressure sensor 19 immediately after the regeneration process.

  A pressure sensor 23 is installed in the intake pipe 21 of the diesel engine 11. In the present embodiment, the pressure sensor 23 is installed in an intake manifold (not shown) in the intake pipe, and outputs a signal corresponding to the intake pressure in the intake manifold (hereinafter referred to as “in manifold pressure”) to the ECU 13.

  Furthermore, although not shown, other sensors (intake pipe pressure sensor) necessary for operating the diesel engine 11 and various devices (such as a turbocharger and a common rail (pressure accumulation chamber)) are attached. ing.

  Next, DPF state detection according to the first embodiment of the present invention will be described.

  FIG. 2 is a graph showing changes in the intake manifold pressure 31 and the DPF differential pressure 33 when the engine 11 is accelerated. The intake manifold pressure 31 is measured by a pressure sensor 23 installed in the intake pipe 21, and the DPF differential pressure 33 is measured by a differential pressure sensor 19 connected upstream and downstream of the DPF 17.

When the engine 11 is accelerated, the amount of intake air into the combustion chamber of the engine 11 increases, so the air flow rate in the intake pipe 21 increases, and the intake manifold pressure 31 also increases accordingly. Assuming that the time required for the intake manifold pressure 31 to increase from A1 (time t1) to A2 (time t2) is t2−t1, the amount of change α per unit time of the intake manifold pressure 31 at this time is obtained from the equation (1). Calculated.
α = (A2−A1) / (t2−t1) (1)
Here, α is expressed as the slope of the straight line 35 connecting the coordinates (t1, A1) and (t2, A2) in FIG.

If the intake amount increases, the exhaust flow rate in the exhaust pipe 15 also increases, and the DPF differential pressure 33 increases accordingly. Further, depending on the positional relationship between the pressure sensor 23 that measures the intake manifold pressure and the differential pressure sensor 19 that measures the DPF differential pressure, the change in the DPF differential pressure 33 has a time delay Δt with respect to the change in the intake manifold pressure 31. Arise. The change amount β of the DPF differential pressure 33 corresponding to the change amount α of the intake manifold pressure 31 is calculated from the equation (2).
β = (B2-B1) / (t2-t1) (2)
Here, B1 is the DPF differential pressure at time t1 + Δt, and B2 is the DPF differential pressure at time t2 + Δt. In FIG. 2, β is represented as the slope of a straight line 37 connecting the coordinates (t1 + Δt, B1) and (t2 + Δt, B2).

  The intake manifold pressure change α and the DPF differential pressure change β take different values depending on the degree of acceleration of the engine. However, the change of the transition due to the acceleration condition is the same, and there is a certain correlation between the change amount α of the intake manifold pressure and the change amount β of the DPF differential pressure.

  In this embodiment, when the engine is accelerated, the DPF state detection is performed using the change amount α of the intake manifold pressure and the change amount β of the DPF differential pressure.

  FIG. 3 is a graph showing the difference in the transition of the DPF differential pressure according to the state of the DPF 17 during acceleration under the same conditions. At this time, since the acceleration state of the engine is the same, the change amount α of the intake manifold pressure is constant.

  The graph 33a shows the DPF differential pressure in a state where the PM accumulation amount is large and the PM is clogged in the DPF (hereinafter referred to as “overdeposition state”). In the over-deposited state 33a, the exhaust gas does not flow easily in the DPF 17 as compared with the normal time 33b, so the DPF differential pressure increases. Accordingly, the amount of change β also increases.

  The graph 33c shows the DPF differential pressure in a state where the DPF is deficient or the like (hereinafter referred to as “deficient state”). In the deficient state 33c, the exhaust gas tends to flow in the DPF 17 as compared with the normal time 33b, so the DPF differential pressure becomes smaller. In accordance with this, the amount of change β also decreases.

  Thus, there is a feature that the change amount β of the DPF differential pressure varies depending on the state of the DPF.

  Here, the ratio γ = α / β between the change amount α of the intake manifold pressure and the change amount β of the DPF differential pressure is taken, and this γ is considered. When DPF 17 is in a deficient state, β decreases, so the denominator of γ decreases, and the value of γ increases. On the other hand, when the DPF is clogged, β increases, so the denominator of γ increases, and the value of γ decreases.

  As shown in FIG. 4, in the deficient state, normal state, and overdeposition state of DPF 17, γ is included in different regions. Therefore, by setting an appropriate determination value, the state of the DPF 17 can be divided into a defective state, a normal state, and an overdeposited state. For example, referring to FIG. 4, since the deficient state of the DPF 17 is separated from other states by the first determination value γa, the failure state of the DPF 17 can be determined. In addition, since the overdeposited state of the DPF 17 is separated from the other states by the second determination value γb, it can be determined that the DPF 17 has accumulated more than the allowable amount of PM.

  In the present embodiment, the state of the DPF 17 is determined based on the value of the ratio γ between the intake manifold pressure change amount α and the DPF differential pressure change amount β during engine acceleration.

  FIG. 5 is a flowchart of processing for detecting the state of the DPF 17 according to the present embodiment.

  In step S101, the intake manifold pressure and the DPF differential pressure are measured. The intake manifold pressure 31 is measured by a pressure sensor 23 installed in the intake pipe 21, and the DPF differential pressure 33 is measured by a differential pressure sensor 19 connected upstream and downstream of the DPF 17.

  In step S103, the change amount α of the intake manifold pressure is calculated by the equation (1), and the change amount β of the DPF differential pressure is calculated by the equation (2). At this time, the time difference Δt between the intake manifold pressure and the DPF differential pressure used in Expression (2) is appropriately determined according to the positional relationship between the pressure sensor and the differential pressure sensor and the intake or exhaust flow rate.

  In step S105, it is confirmed whether the change amount α of the intake manifold pressure is equal to or greater than a predetermined value. When it is equal to or greater than the predetermined value, it is determined that the engine is in a transient operation state, and the process proceeds to step S107. When it is less than the predetermined value, the process is terminated.

  In step S107, the ratio γ = α / β between the variation amount α of the intake manifold pressure and the variation amount β of the DPF differential pressure is calculated.

  In step S109, it is confirmed whether γ is greater than a predetermined first determination value γa. When γ is larger than γa, the process proceeds to step S111, and it is determined that the DPF has failed. When γ is γa or less, the process proceeds to step S113.

  In step S113, it is confirmed whether γ is larger than a predetermined determination value γb. When γ is larger than γb, the process proceeds to step S115 and it is determined that the DPF is normal. When γ is equal to or less than γb, the process proceeds to step S117, where it is determined that the DPF is excessively deposited, and the regeneration process is executed.

  Thus, this embodiment implements DPF state detection during engine acceleration. Since the transient operation state of the engine, such as during acceleration, frequently occurs during operation, the DPF state detection method according to the present invention can frequently detect the DPF state during operation.

  Next, a second embodiment of the present invention will be described.

  The basic concept of the DPF state detection method according to the present embodiment is the same as that of the first embodiment, but the determination method for determining the state is different.

  FIG. 6 is a diagram illustrating the first determination value γa (pm) and the second determination value γb (ash) in the present embodiment. As described above with reference to FIG. 4, the state of the DPF can be detected by the ratio γ = α / β of the change amount α of the intake manifold pressure and the change amount β of the DPF differential pressure. However, when a failure such as a defect occurs in the over-deposited state, for example, in the region indicated by reference numeral 39 in FIG. 6, the exhaust gas does not flow easily in the DPF as in the normal state. There may be a situation where the value does not increase compared to the normal state. In this case, if the first determination value γa is set to a constant, the failure state of the DPF 17 may not be determined.

  Therefore, in the present embodiment, the first determination value used for determining the DPF failure is a function γa (pm) that changes according to the PM accumulation amount pm. As shown in FIG. 6, the first determination value γa (pm) is set to take a smaller value as the PM deposition amount pm increases.

  In addition, after the DPF regeneration process, unburned residue (ash) such as oil components in the exhaust gas remains in the DPF. Ashes are deposited in the DPF every time the regeneration process is repeated. The change amount β of the DPF differential pressure used for determining the state of the DPF in this embodiment is also affected by the residual amount of ash in addition to PM. That is, as the residual amount of ash increases, the change amount β of the DPF differential pressure corresponding to the same PM accumulation amount takes a larger value, so that γ = α / β takes a smaller value. Become. When the second determination value γb is set to a constant, the DPF overdeposition state is erroneously determined due to the influence of the residual amount of ash even though the PM has not yet accumulated in the DPF so as to perform the regeneration process. There is a possibility.

  Therefore, in the present embodiment, the second determination value for determining DPF overdeposition is a function γb (ash) that changes in accordance with the residual ash amount ash. As shown in FIG. 6, the second determination value γb (ash) is set to take a smaller value as the ash residual amount ash increases.

  FIG. 7 is a flowchart of the DPF state detection process according to the present embodiment.

  In step S201, the intake manifold pressure and the DPF differential pressure are measured. The intake manifold pressure 31 is measured by a pressure sensor 23 installed in the intake pipe 21, and the DPF differential pressure 33 is measured by a differential pressure sensor 19 connected upstream and downstream of the DPF 17.

  In step S203, the change amount α of the intake manifold pressure is calculated by the equation (1), and the change amount β of the DPF differential pressure is calculated by the equation (2). At this time, the time difference Δt between the intake manifold pressure and the DPF differential pressure used in Expression (2) is appropriately determined according to the positional relationship between the pressure sensor and the differential pressure sensor and the intake or exhaust flow rate.

  In step S205, the PM accumulation amount pm and the ash residual amount ash of the DPF are estimated. The PM deposition amount pm is calculated based on the intake manifold pressure, the DPF differential pressure, or the like using a known method as described in Patent Document 2, for example. The ash residual amount ash is calculated based on, for example, the DPF differential pressure immediately after the regeneration process is performed. The ash residual amount ash is calculated based on the difference Δγ between the ratio γ of the intake manifold pressure change α and the DPF differential pressure change β immediately after the regeneration process and the DPF γ corresponding to a new product. Also good. The ash residual amount ash is calculated every time the reproduction process is performed, and is stored in the memory 13c.

  In step S207, the first determination value γa (pm) is set according to the estimated PM accumulation amount pm, and the second determination value γb (ash) is set according to the estimated ash residual amount ash. .

  In step S209, it is confirmed whether the intake manifold pressure change amount α is greater than or equal to a predetermined value. When it is equal to or greater than the predetermined value, it is determined that the engine is in a transient operation state, and the process proceeds to step S211. When it is less than the predetermined value, the process is terminated.

  In step S211, a ratio γ = α / β of the intake manifold pressure change amount α and the DPF differential pressure change amount β is calculated.

  In step S213, it is confirmed whether γ is larger than the first determination value γa (pm). When γ is larger than γa (pm), the process proceeds to step S215, and it is determined that the DPF has failed. When γ is γa (pm) or less, the process proceeds to step S217.

  In step S217, it is confirmed whether γ is larger than the second determination value γb (ash). When γ is larger than γb (ash), the process proceeds to step S219, and it is determined that the DPF is normal. When γ is equal to or less than γb (ash), the process proceeds to step S221, where it is determined that the DPF is excessively deposited, and the regeneration process is executed.

  As described above, in this embodiment, since the determination value is changed according to the PM accumulation amount and the ash residual amount in the DPF, the state of the DPF is accurately detected even when a large amount of PM or ash is accumulated in the DPF. Can be done.

  Next, a third embodiment of the present invention will be described.

  FIG. 8 is a diagram illustrating a transition of the value of γ calculated for each cycle of the DPF state detection process when the DPF is normal and when the failure occurs. As shown in FIG. 8A, when the DPF is normal, γ changes with no significant difference between the periods. On the other hand, as shown in FIG. 8 (b), when the DPF fails, the flow of exhaust gas in the DPF is unstable due to the deficiency, so that the change amount β of the DPF differential pressure also becomes unstable. For this reason, there is a feature that variation of γ calculated for each processing loop becomes large at the time of DPF failure.

  In the present embodiment, the difference between the current value of γ and the previous value is integrated a predetermined number of times, and the DPF state is detected when the integrated value exceeds a predetermined determination value. This integrated value represents the degree of variation in γ, and the larger the integrated value, the larger the variation in γ.

  FIG. 9 is a flowchart of the DPF state detection process according to the present embodiment.

  In step S301, the intake manifold pressure and the DPF differential pressure are measured. The intake manifold pressure 31 is measured by a pressure sensor 23 installed in the intake pipe 21, and the DPF differential pressure 33 is measured by a differential pressure sensor 19 connected upstream and downstream of the DPF 17.

  In step S303, the change amount α of the intake manifold pressure is calculated by the equation (1), and the change amount β of the DPF differential pressure is calculated by the equation (2). At this time, the time difference Δt between the intake manifold pressure and the DPF differential pressure used in Expression (2) is appropriately determined according to the positional relationship between the pressure sensor and the differential pressure sensor and the intake or exhaust flow rate.

  In step S305, it is confirmed whether the intake manifold pressure change amount α is greater than or equal to a predetermined value. When the value is equal to or greater than the predetermined value, it is determined that the engine is in a transient operation state, and the process proceeds to step S307. When it is less than the predetermined value, the process is terminated.

  In step S307, the ratio γ (t) = α / β of the intake manifold pressure change amount α and the DPF differential pressure change amount β is calculated.

  In step S309, the difference Δγ = γ (t) −γ (t−1) between the current value γ (t) of γ and the previous value γ (t−1) is calculated.

In step S311, whether the square sum Shigumaderutaganma ² of a predetermined number of times of the difference Δγ is larger than a predetermined judgment value is confirmed. When the square sum Shigumaderutaganma ² is greater than the determination value, the process proceeds to step S313, it is determined that the DPF failure. When it is equal to or smaller than the determination value, the process proceeds to step S315, and it is determined that the DPF is normal.

  The specific embodiments of the present invention have been described above. However, the present invention is not limited to such examples.

  In the above-described embodiment, the intake manifold pressure is used to determine the state of the DPF, but any signal having a correlation with the exhaust flow rate may be used. For example, the present invention can be implemented even if the pressure in the exhaust pipe upstream of the DPF is used, and the intake flow rate or the exhaust flow rate may be directly measured and used.

  In the above-described embodiment, the engine acceleration is exemplified as the transient state in which the state of the DPF 102 is detected. However, the present invention can be implemented even when the engine is decelerated.

  Moreover, although the diesel engine was demonstrated in the above-mentioned embodiment, this invention is applicable similarly also with a gasoline engine.

1 is an overall configuration diagram of a diesel engine mounted on a vehicle and a control device thereof according to an embodiment of the present invention. It is a graph which shows transition of an intake manifold pressure and a DPF differential pressure at the time of engine acceleration. It is a graph which shows the behavior of DPF differential pressure according to the state of DPF, and change amount (beta) at the time of acceleration of the same conditions. It is a figure which shows 1st determination value (gamma) a and 2nd determination value (gamma) b in the 1st Embodiment of this invention. It is a flowchart of the DPF state detection process by the 1st Embodiment of this invention. It is a figure which shows 1st determination value (gamma) a (pm) and 2nd determination value (gamma) b (ash) in the 2nd Embodiment of this invention. It is a flowchart of the DPF state detection process by the 2nd Embodiment of this invention. It is a figure which shows transition of (gamma) calculated for every period of a DPF state detection process at the time of DPF normal time and a failure. It is a flowchart of the DPF state detection process by the 3rd Embodiment of this invention.

Explanation of symbols

13 Electronic control unit (ECU)
17 Diesel particulate filter (DPF)
19 Differential pressure sensor 23 Pressure sensor

Claims (5)

A particulate filter provided in an exhaust system of an internal combustion engine;
An exhaust flow rate detecting means for detecting a signal correlated with the exhaust flow rate of the internal combustion engine;
Differential pressure detecting means for detecting a differential pressure across the particulate filter;
A state in which the state of the particulate filter is determined by comparing a ratio of the change amount of the signal correlated with the exhaust flow rate and the change amount of the differential pressure with a predetermined threshold value during the transition of the internal combustion engine. A determination means;
A state detection device for a particulate filter of an internal combustion engine, comprising:   The particulate filter state detection device according to claim 1, wherein the signal correlated with the exhaust flow rate is an intake pipe pressure of the internal combustion engine. The state determining means compares the ratio of the amount of change in the signal correlated with the exhaust flow rate and the amount of change in the differential pressure with a first threshold value to determine whether the particulate filter has failed,
A ratio of a change amount of a signal correlated with the exhaust flow rate and a change amount of the differential pressure is compared with a second threshold value to determine that the particulates in the particulate filter are over-deposited; The particulate filter state detection device according to claim 1.   The first threshold value is set according to the accumulation amount of the particulates in the particulate filter, and the second threshold value is set according to the residual amount of ash in the particulate filter. The particulate filter state detection device according to claim 3.   The state determination means integrates a deviation between a previous value and a current value of a ratio between a change amount of a signal correlated with the exhaust gas flow rate and a change amount of the differential pressure, and the integrated deviation is a predetermined threshold value. The particulate filter state detection device according to claim 1, wherein a failure of the particulate filter is determined at the time described above.

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